SMALL-MOLECULE INHIBITORS OF lAPs BASED ON MIMICKING SMAC. Inhibitor of Apoptosis Proteins (LAPs) are endogenous antagonists of Caspase-family cell death proteases, which are over-expressed in many cancers, creating road-blocks to tumor cell eradication. The purpose of our proposed project is to generate, characterize, and test in preclinical models of cancer small-molecule chemical inhibitors of lAPs. To accomplish this goal, we have adopted a drug screening strategy based on attempts to mimic an endogenous antagonist of lAPs, known as SMAC. The SMAC protein binds specific BIR domains in target lAPs via an evolutionarily conserved tetrapeptide motif, thus displacing Caspase and promoting apoptosis. Proof of concept experiments using tetrapeptide derived from SMAC suggest a strategy for smallmolecule drug discovery based on compounds that mimic SMAC. The goal of this proposal is to generate and characterize small-molecule drugs that mimic SMAC, thus sensitizing cancer cells to apoptosis by targeting lAP-family proteins. Using high throughput screening assays already developed by the project team, we will screen traditional and mixture-based combinatorial chemical libraries for non-peptidyl SMAC mimics. These compounds will be profiled for cellular activity using genetically engineered tumor cell lines. Then, the compounds will be optimized through medicinal chemistry approaches in conjunction with protein structure information. Our aim is to generate novel chemical entities that demonstrate potent mechanism-based activity against lAPs, advancing these compounds into in vitro cell-based and in vivo tumor xenograft models, and thus laying a foundation for eventual applications in clinical trials for treatment of cancer.